1. Field of the Invention
The present invention is related to a method of analyzing measurement report events, and more particularly, to a method of analyzing non-acknowledgement of a network in response to measurement reports.
2. Description of the Prior Art
In a Universal Mobile Telecommunication System (UMTS) defined by the third Generation Partnership Project (3GPP), mobility management mainly includes cell selection/reselection, handover and related measurements. Handover refers to the transfer process of management from a current serving cell to a target cell and is performed in all cellular mobile communication systems. There are two types of handover: hard handover and soft handover. Hard handover may be performed in all non-CDMA (code division multiple access) systems. For example, in a time division multiple access (TDMA) system, the current connection is broken before making a new connection to the target cell. Such break-before-make hard handover only requires simple hardware structure, but suffers from high call drop rate. Soft handover may be performed in all CDMA systems which adopt orthogonal codes and rake receivers. Such make-before-break soft handover can reduce call drop rate during handover, but requires more complicated hardware structure or algorithm.
The cells around a user equipment (UE) can be categorized in 3 different sets: active set, candidate set and monitored set. A cell of the active set is configured to establish connection with a mobile device during handover. A cell of the candidate set does not establish connection with a mobile device during handover, but its signal quality is qualified to be included in the active set. A cell of the monitored set does not have signal quality qualified to be included in the active set. The UE is configured to measure the signals of all cells within its communication range and perform handover accordingly. Soft handover includes three major modes: radio link addition, radio link removal, and radio link replacement. The decision of whether a cell belongs to the active set or the monitored set is made by the UE. According to corresponding trigger conditions, the UE may add an unconnected cell into the active set or remove a connecting cell from the active set.
The network is configured to send measurement criteria to the UE via broadcast control channel (BCCH) for managing handover, radio bearer control (RBC) and positioning. The UE is then configured to evaluate whether the signals of the cells in the active set and the monitored set satisfy trigger conditions according the parameters provided by the network. The radio network controller (RNC) is notified when a trigger condition is satisfied for determining whether a corresponding handover should be performed.
When detecting a cell with better signal quality, the UE may send a corresponding measurement report event for updating the active set. However, the network may not be able to respond to the measurement report event for some reason, such as due to transmission failure or lack of storage space. Without the notification of updating the active set from the network, the UE may keep sending the same measurement report event for a while and fail to perform the appropriate handover. If the signal quality of the current cell somehow degrades and results in call drop, the user is unable to know the cause of communication failure.